Method of making a reusable, tear-resistant polyolefin-paper laminate

ABSTRACT

A tough, tear-resistant, reusable, well-bonded polyolefin-paper laminate is formed by laminating a polyolefin film, preferably oriented, to a paper substrate by means of a melt of a polymer containing the same olefin as used in the film.

nited States Patent n91 Peterson et a1.

METHOD OF MAKING A REUSABLE, TEAR-RESISTANT- POLYOLEFlN-PAPER LAMINATEinventors: Lenarl A. Peterson: John G. Finley.

both 01' ('hicugn. lll.

Assigncc: Phillips Petroleum Company. Bartlcsville, Okla. Filed: Mar.22, 1973 Appl. No.: 344,024

Related US. Application Data Division of Ser. No. 13,413, Feb. 24, 1970,Pat. No. 3,752,732.

US. Cl 156/244, 156/280, 156/289, 156/322, 156/324, 156/334, 161/208,161/209, 16'1/250, 161/252, 161/402 Int. Cl B32b 31/30, B32b 27/10, C09j5/02 Field of Searh....; 117/76 P; 156/244, 280,

1 1 Jan. 28, 1975 References Cited UNlTED STATES PATENTS 3,403,0459/1968 Erickson et al 1 17/68 3,547,682 12/1970 Erb 1 [17/75 3.5531173l/197l Rzlusing ct ul. .1 161/166 3,775,549 ll/l973 Mutsuda ct ill.174/25 R FOREIGN PATENTS OR APPLICATIONS 917,276 l/l963 (jreu! Britain[61/252 919,065 2/1963 Great Britain... 1,213,991

4/1966 Germany 161/247 Primary Examiner-Charles E. Van Horn AssistantExaminer-Robert A. Dawson 57 ABSTRACT A tough, tear-resistant, reusable,well-bonded polyolefin-paper laminate is formed by laminating apolyolefin film, preferably oriented, to a paper substrate'by means of amelt of a polymerconuaining the same olefin as used in the film.

17 Claims, 3 Drawing Figures METHOD OF MAKING A REUSABLE, TEAR-RESISTANTPOLYOLEFIN-PAPER I LAMINATE This application is a division ofapplication Ser. No. 13,413, filed Feb. 24, 1970, now U.S. Pat. No.3,752,732.

This invention relates to a reusable polyolefinbonded-to-paperstructure. In another aspect,-it relates to an improved method ofbonding a polyolefin to a paper substrate.

A presently used method of preparing cured adhesive compositions is tocoat the adhesive onto a supported polyolefin film, apply a backing orother structure to the adhesive, then cure the adhesive at a suitabletemperature. After curing, the supported polyolefin film is strippedoff, and the adhesive structure is used in corn plasters, bunionpatches,and other applications in the pressure sensitive tape fieldincluding pharmaceutical requirements. Concerns preparing such pressuresensitive tape assembliesprefer a release paper that is reusable.Single-use supports are relatively expensive and added needlessly toproduct costs. Efforts to reuse such supports usually are ine ffective,due to poor tearing characteristics, and particularly attributable toinsufficient adhesion of the polycoating to the base stock.

Needed is a structure that can be used repeatedly, used again and again.To meet this, the polyolefin film not only must be well supported, butit must be unusually well-bonded or laminated to the base stock. And,the structure must have good resistance to tearing, as well as goodresistance to separation of the polycoating from the base stock. Such astructure can be used repeatedly, greatly reducing the cost of theultimately prepared pressure sensitive tapes and similar adhesive coatedstructures.

This need is fully met by our invention. The structure of our inventionis a polyolefin film well bonded to a paper substrate. The bonding iseffected by use of a melt of a polyolefin prepared at least in part ofthe same olefin or combination of olefins common to the polymer used inthis film to be bonded. The film, pref erably an oriented film,optionally is release coated on its outer surface. The substrate, also,can be optionally release coated on its exposed surface.

The structure or our invention isso effective that it is reusable 10,even times. Thus, the cost of the user of his support is one-tenth orone-fifteenth what it has been heretofore.

It is an object of our invention to provide a repeatedly reusable bondedpolyolefin-paper structure.

Other aspects, objects, and the several advantages of our invention willbe apparent to one skilled in the art from our description including thefigures of our drawing and from our appended claims. I

Our invention can be more readily understood by referring immediately.to the attached drawing which shows three figures. These figures showthe structure of our invention, together with a method of preparing thestructure.

FIG. I illustrates the basic structure of our invention and shows incombination a paper base, the bonding polyolefin, and the'bondedpolyolefin film.

FIG. 2 illustrates the method of forming the structure of our inventionby melt bonding a polyolefin film with a polyolefin melt to a paperbase.

FIG. 3 adds to the basic structure of FIG. 1 optional release coatingson the external surfaces of both the base and the film.

In FIG. I the first layer 1 is the base or substrate or backing sheet.The next layer 2 is the bonding layer formed from a melt of apolyolefin, and this also is shown with a merging area 3 as it bondswith the polyolefin film 4 itself. The bond between the polyolefin filmand the base or substrate is sufficiently strong for the entirestructure to be repeatedly processed, receiving adhesive andsuperstructures, curing of such adhesive, stripping of curedadhesive-superstructure combinations, and reused again and again as asupport structure.

A variety of materials can be employed as a base or substrate. Fibrouscellulosic sheet material are preferred, such as bleached paper and thelike as well as papers made from pulps prepared by chemical, mechanical,or chemical-mechanical processes other than the Kraft process. Kraftpaper is particularly suitable in general because of its overallproperties. We prefer a Kraft paper with a basis of from pounds per3,000 square foot-ream upward to 100 pounds per ream. The

' substrate to be used should have sufficient rigidity so in continuedreuse.

While Kraft-type paper is preferred, other materials can be utilizedsuch as Holland cloth; or glassine, which is a super-calendered paperwhose name is derived from its peculiary glossy surface, high densityand transparency.

Usually, the base is pretreated which tends to assist the polyolefinmelt to bond with the paper. The pretreatment is not a necessity, sinceacceptable bonding to unpretreated paper often can be attained by usinga polyolefin melt temperature in the upper part of the recommended rangeas discussed hereinafter.

In discussing the polyolefins useful in bonding and for the film, theterm polyolefin refers to the polymeric material of a l-olefinof from 2to 8 carbon atoms per molecule, and includes copolymers between two ormore thereof, and further includes copolymers having up to 25 weight percent of monomers commonly copolymerized therewith.

The preferred polymers are either homopolymers of propylene orcopolymers of propylene with ethylene. In the experience, thepolypropylenefilms have been preferred since they tend to betterwithstand temperatures at which the later applied adhesive is cured inpreparing the pressure sensitive tapes and-the like.

Most preferred are the oriented films, i.e., stretched from 2 to 12times relative to the original film dimension, resulting in a tensilestrength of from 8,000 to 20,000 psi. Most desired are those films whichare biaxially oriented.

' for ethylene polymers); the density should range from same as that ofthe primary monomer in the polyolefin film, so as to obtain optimumadhesion and bonding propertiesQSecondly, the polyolefin used for themelt preferably should have a high melt flow so as to minimizedisorientation of the film where an oriented film is utilized, thoughthis'requirement is not a necessity when a non-oriented film isutilized, preferably should be higher than that of the film, and can befrom about 20 to 100, more preferably from 50 to 80.

The polyolefin bonding melt is extruded at a melt temperature offrom 350to 700 F., more usually from 350 to 650 F., preferably 450 to 600 F. Theamount of the polyolefin melt applied will usually be within a range offrom 3 to l6 pounds of the melt per 3,000 square foot-ram of the base,more usually between 8 and 14 pounds per ream.

As discussed above, the higher portion of the melt temperature range,above 600 F., can be used if desired where an untreated paper base is tobe bonded, since the higher melt extrusion temperature gives improvedbonding with untreated bases. A caution should be exercised, of course,.that if the melt temperature is too hot, it can tend to disorient thefilm, especially films below about 0.2 mils thick. Therefore, the melttemperature preferably is maintained below 600 F. and a pretreatedsubstrate is preferred so as to obtain most effective bonding at lowermelt temperatures, and films thicker than 02 mils are preferred.

Another method to improve bonding is to preheat the substrate, and thepaper substrate can be preheated to any temperature up to below adarkening or loss-ofstrength stage for the particular base utilized. Apreheated base tends to bond more effectively to the melts hence thereis less tendency for a cooled surface melt film to develop and possiblyinterfere with bonding.

Where the base stock is to be pretreated, pretreatment can be with anysuitable primer known to the art.

One suitable primer is prepared from a polyalkyleneimine such as apolyethyleneimine which is available from Eastman Chemical Products,Inc., Subsidiaryof Eastman Kodak Co., Kingsport, Tenn. Such pretreatmentis usually applied by means of a gravure roller using a 50 to 1,000 footper minute line speed, more usually of the order of 200 feet per minute,and applying at a rate of from about 0.5 to 5.0 pounds per ream on a wetbasis with a hydrocarbon solvent such as toluene or n-hexane, or at therate of 0.01 to 0.l pounds per ream on a dry solids basis. The materialusually is applied on a basis of about 0.04 pounds of dry solid perpound of solution including solvent.

Referring now to our FIG. 2, this illustrates in basic fashion theprocess of lamination utilizing materials that .we have described above.The paper is shown as 11, the polyolefin melt 12 to be supplied as abonding web or extrudate 13 for bonding, and the polyolefin film 14. Thethree components are brought together so that the melt is brought to thenip 15 of rollers 16 and 17. Roller 16 normally will be a chill rollthrough which is circulated water at a temperature of 60 to 75 F. androller 17 a rubber backup roll. It is preferred to use a roll pressurein the range of 10 to 100 psi, preferably 40 to psi. These rollers pressthe combination of the paper base 11, bonding polyolefin melt 12, andpolyolefin film 14 together, resulting in the structure 18 of ourinvention. Line speed usually will be in the range of 50 to l,000 linearfeet per minute, more usually on the order of 200 feet per minute. Linespeeds can be adjusted according to the'ability of the equipment tohandle the materials. extrusion rate of themelt to be utilized, and thelike.

The basic structure of our invention optionally can be release coated oneither the exposed outer surface of the polyolefin film, or on theexposed outer surface of the base or substrate, or both. FIG. 3 showsthe basic structure of paper 1, bonding polyolefin 2, merging area 3,bonded polyolefin film 4, and additionally shows coating 5 and 5, eachbeing a release coating applied to the outer surface as shown in thedrawing.

These release coatings are curable silicones, often called theorganopolysiloxanes. They have the general repeating structure where Ris a hydrocarbon radical and one of the R groups can be hydrogen. R canbe any suitable monovalent hydrocarbon radical such as alkyl,cycloalkyl, aryl, alkaryl, and aralkyl, or combinations thereof.Preferably, each R is selected from alkyl radicals containing from 1 to6 carbon atoms, and phenyl. The methyl radical is frequently employed insuch compositions. In some compositions an ether linkage 0- issubstituted for one of the R groups in order to provide for additionalcross-linking effects. Thesev organopolysiloxane release coatings andmethods of application of same are well known to the art.

The release layers applied to the outer surface of the base paper or tothe outer surface of the polyolefin film, or both, are desirable whereparticular applications of the entire composition assembly are intended.The above described organopolysiloxane in solution are applied inamounts, on a dry basis, within the range of from 0.03 to 0.4,preferably 0.06 to 0.3 pounds per ream. Most desirably, such releasecoating is applied to the outer surface of the polyolefin film, sincethe anticipated purpose of the structure of our invention is to be usedto support an adhesive which is coated on the polyolefin of ourstructure, a backing such as corn plaster composition and the like isapplied, or tire patching or a myriad of other useful applications, andthe adhesive then is cured at a-fairly high temperature. After curing,it is desired that the users own construction including cured adhesivebe readily stripped from the structure of our invention, and thestructure of our invention then reused multiple times. For this purpose,a suitable release coating 'on the polyolefin is desired.

Rather frequently, the customer, after applying his adhesive, andapplying his own construction or superstructure, rolls the entireassembly for convenience in curing. The optional release coating on thepaper or substrate outer surface helps avoid any sticking problems. Ofcourse, this curing method is not necessary. since the entire assemblycan be cured in line at suitable temperatures and the bonded polyolefinstructure EXAMPLE I A '50 pound per ream extensible Kraft papersubstrate was used in this run. The paper was pretreated in line usingthe hereinbefore described Eastman Chemical Products, Inc. primer, apolyethyleneimine solution, which was applied at the rate of 2 pounds ofwet solids per ream of paper, equivalent to 0.04 pounds of dry solidsper ream. This pretreating composition was received at 5-percent solidsand was reduced to 2 percent solids for actual application using tolueneas solvent with application to thepaper by a 150 quadrangular gravureroller with cells 24 microns deep at a line speed of 200 linear feet perminute. The polyolefin film used was a 50 gauge biaxially orientedpoly-propylene film. The polyolefin film, i.e., the

polypropylene film in this run, was corona treated on one side. Theuntreated side was then bonded to the paper base using as bonding agenta melt of a propylene-ethylene copolymen The melt flow of thepolypropylene film was 4, and the density of the polypropylene in thefilm was 0.90 gms/cc. Melt flow of the polypropylene in the melt wasabout 70, and the density of the polypropylene used in the melt was 0.90gms/cc. A melt temperature of approximately 575 F. was used, and l2pounds of the melt was applied per ream of base'to achieve the bondmg.

After bonding,'the.composition was overcoated in line with anorganopolysiloxane release coating using a 150 quadrangular cell, of 24microns depth, gravure cylinder. The organopolysiloxane was applied as asolu' tion in toluene as diluent. X-ray examination of samples from llrolls indicated that the amount of organopolysiloxane applied, on a drybasis, ranged from 0.23 8

to 0,285 pounds per ream.

Examination of the release characteristics of the silicone coated sideof the final composition showed a release of 20 grams per inchwidth at180 pullback using a J&J patch test, Tappi RC-283. The release broadlydesired is fromil to 75 grams per inch width at 180 pullback, preferredrange is from 5 to 50grams per inch width. Eleven rolls showed a rangeof 9 to 19 grams per inch width. Thus, the bonded supported polyolefinfilm, well bonded and supported for processing and repeatedapplications, is readily strippable from adhesive structure subsequentlyadded by the customer, and hence can be readily reused. Examination ofthe laminate disclosed excellent adhesion of film to paper whichstrongly resisted delamination.

EXAMPLE n the bonding strength of the laminate, were essentially thesame as reported above. This example shows the ment, and that it can beproduced readily and consistently. The produced structures have beenused from 10 to 15 times without delamination.

I repeatability of our invention, on commercial equip- The bondedpolyolefin-paper composition of our invention is useful and versatile inthe production of many types of products, as will be observed from theforegoing discussion. Thecomposition is one that can be readily used andreused time and again, as a support for adhesive based superstructurespending assembly and processing of same. Such adhesive basedsuperstructures, after curing and necessary processing, can be readilyreleased or stripped from our polyolefin bonded laminate, and thepolyolefin bonded laminate then reused repeatedly.

Reasonable variations and modifications of our invention are possiblewithin the scope of this disclosure, yet without departing from thescope and spirit thereof as discussed hereinabove and in the claims thatfollow.

We claim:

1. A process for preparing a bonded polymonoolefinpaper laminatecomprising in order a polymonoolefin film, a polymonoolefin bondinglayer, and a fibrous cellulosic support sheet, and suited to repeatedreuse, which comprisesf a. contacting a moving continuousfibrous,cellulosic sheet and a moving continuous polymonoolefin film, I b.continuously extruding a hot melt of a polymonoolefin to the area ofcontact between said sheet and said film, wherein'said film and saidmelt each are polymonoolefin polymers containing as a major component acommon l-monoolefin monomer, and c. pressing together by said rollermeans said sheet, melt and film, and thereby forming said laminate;

wherein said polymonoolefin of said film is characterized by a melt flowor index of 0.2 to 20, and said polymonoolefin of said melt ischaracterized by a melt flow or index higher than that of said film andfurther in the range 20 to 100.

2. A process according to claim 1 wherein each said polymonoolefin is apolymer of at leastone monoolefin of 2 to 8 carbon atoms per moleculeand 0 to 25'weight percent of a monomer copolymerizable therewith.

3. A process according to claim 2 wherein said film Kraft paper weighing25 to 100 pounds per 3,000 square foot-ream.

4. A process according to claim 3 wherein said paper is preheated andsaid melt temperatuure is above 600 is an oriented film.

6. A process according to claim 5 wherein said polyolefins are polymersof propylene; said film is biaxially oriented; said Kraft paper ispretreated with polyalkylene prior to said step (a); said film M.F. isabout 1 to 6, and said melt MP. is about 50 to and said process includesthe further step of applying a curable organopolysiloxane releasecoating onto at least one of the outer surface of said film and theouter surface of said sheet.

7. A process for preparing at high line speeds apolymonoolefin-substrate laminate suited to repeated reuse whichcomprises laminating a polymonoolefin 5. A process according to claim 3wherein said film film to a fibrous cellulosic substrate by means of apolymonoolefin melt, which process comprises:

a. continuously contacting a moving web of said substrate and a movingpolymonoolefin film,

. b. continuously extruding a polymonoolefin melt bonding layer atelevated temperature to the area of said contact between said substrateand said film,

c. pressing together said substrate, said bonding layer melt, and saidfilm, thereby forming said polymonoolefin-substrate laminate,

' wherein said polymonoolefin bonding layer and said polymonoolefin filmeach contain as a major component a common l-monoolefin monomer of 2 to8 carbon atoms per molecule, and each can contain up to 25 weightpercent of monomer copolymerizable therewith, wherein saidpolymonoolefin of said bonding layer is characterized by melt flow ofabout 50 to 80, and said polymonoolefinof said film is characterized bymelt flow of about 1 to 6.

8. The process according to claim 7 wherein said polyolefin film furtheris characterized by a density of about 0.89 to 0.97 gm/cc.

9. A process according to claim 7 wherein said film has a thickness ofabout 0.2 to 5 mils.

- 10. The process according to claim 7 wherein said film is an orientedfilm.

11. The process according to claim 7 wherein said substrate or said filmor both are release coated on the exposed outer surface thereof, andsaid release coating is an organopolysiloxane applied in an amount so asto provide about 0.03 to 0.4 pounds per ream 'on a dry-basis. v

12. The process according to claim 7 wherein said substrate is preheated'to a temperature below a loss of strength stage for said substrate.

. 13. The process according to claim 7 wherein said polymonoolefinbonding melt is melt extruded at a melt temperature of about 350 to 700F., and applied in a range of about 3 to l6 pounds of said melt per 3000square foot-ream of said substrate.

14. The process according to claim 13 wherein said substrate ispretreated with a polyalkyleneimine at a rate of about 0.5 to 5 poundsper ream employing said polyalkyleneimine as a hydrocarbon solutionthereof, so as to apply about 0.01 to 0.] pound per ream on a dry solidsbasis.

15. The process according to claim 14 wherein said substrate is a Kraftpaper, said film is a biaxially oriented polypropylene fil'rn, said meltflow bonding is a polypropylene.

16. The process of claim 7 wherein each said polymonooolefin is selectedfrom homopolymers of propylene and copolymers of ethylene-propylene.

17. The process of claim 1 wherein said sheet is conveyed by a firstroller means; said film is conveyed by a second roller means; said firstand second roller means define or nip area therebetween, and said areaof contact is defined by said nip area.

1. A PROCESS FOR PREPARING A BONDED POLYMONOOLEFIN-PAPER LAMINATECOMPRISING IN ORDER A POLYMONOOLEFIN FILM, A POLYMONOOLEFIN BONDINGLAYER, AND A FIBROUS CELLULOSIC SUPPORT SHEET, AND SUITED TO REPEATEDREUSE, WHICH COMPRISES: A. CONTACTING A MOVING CONTINOUS POLYMONOOLEFINFILM, AND A MOVING CONTINOUS POLYMONOOELFIN FILM, B. CONTINOUSLYEXTRUDING A HOT MELT OF A POLYMOONELFIN TO THE AREA OF CONTACT BETWEENSAID SHEET AND SAID FILM WHEREIN SAID FILM AND SAID MELT EACH AREPOLYMONOOLEFIN POLYMERS CONTAINING AS A MAJOR COMPONENT A COMMON1-MONOOLEFIN MONOMER, AND C. PRESSING TOGETHER BY SAID ROLLER MEANS SAIDSHEET, MELT AND FILM, AND THEREBY FORMING SAID LAMINATE; WHEREIN SAIDPOLYMONOOLEFIN OF SAID FILM IS CHARACTERIZED BY A MELT FLOW OR INDEX OF0.2 TO 20, AND SAID POLYMONOOLEFIN OF SAID MELT IS CHARACTERIZED BY AMELT FLOW OR INDEX HIGHER THAN THAT OF SAID FILM AND FURTHER IN THERANGE 20 TO
 100. 2. A process according to claim 1 wherein each saidpolymonoolefin is a polymer of at least one monoolefin of 2 to 8 carbonatoms per molecule and 0 to 25 weight percent of a monomercopolymerizable therewith.
 3. A process according to claim 2 whereinsaid film has a thickness of 0.2 to 5 mils and is prepared from apolymonoolefin with a density of 0.89 to 0.97 gms/cc; wherein said meltpolymonoolefin is applied at a melt temperature of 350* to 700* F., andat a rate of 3 to 16 pounds per ream of paper; and wherein said sheet isa Kraft paper weighing 25 to 100 pounds per 3,000 square foot-ream.
 4. Aprocess according to claim 3 wherein said paper is preheated and saidmelt temperatuure is above 600* F.
 5. A process according to claim 3wherein said film is an oriented film.
 6. A process according to claim 5wherein said polyolefins are polymers of propylene; said film isbiaxially oriented; said Kraft paper is pretreated with polyalkyleneprior to said step (a); said film M.F. is about 1 to 6, and said meltM.F. is about 50 to 80; and said process includes the further step ofapplying a curable organopolysiloxane release coating onto at least oneof the outer surface of said film and the outer surface of said sheet.7. A process for preparing at high line speeds apolymonoolefin-substrate laminate suited to repeated reuse whichcomprises laminating a polymonoolefin film to a fibrous cellulosicsubstrate by means of a polymonoolefin melt, which process comprises: a.continuously contacting a moving web of said substrate and a movingpolymonoolefin film, b. continuously extruding a polymonoolefin meltbonding layer at elevated temperature to the area of said contactbetween said substrate and said film, c. pressing together saidsubstrate, said bonding layer melt, and said film, thereby forming saidpolymonoolefin-substrate laminate, wherein said polymonoolefin bondinglayer and said polymonoolefin film each contain as a major component acommon 1-monoolefin monomer of 2 to 8 carbon atoms per molecule, andeach can contain up to 25 weight percent of monomer copolymerizabletherewith, wherein said polymonoolefin of said bonding layer ischaracterized by melt flow of about 50 to 80, and said polymonoolefin ofsaid film is characterized by melt flow of about 1 to
 6. 8. The processaccording to claim 7 wherein said polyolefin film further ischaracterized by a density of about 0.89 to 0.97 gm/cc.
 9. A processaccording to claim 7 wherein said film has a thickness of about 0.2 to 5mils.
 10. The process according to claim 7 wherein said film is anoriented film.
 11. The process according to claim 7 wherein saidsubstrate or said film or both are release coated on the exposed outersurface thereof, and said release coating is an organopolysiloxaneapplied in an amount so as to provide about 0.03 to 0.4 pounds per reamon a dry basis.
 12. The process according to claim 7 wherein saidsubstrate is preheated to a temperature below a loss of strength stagefor said substrate.
 13. The process according to claim 7 wherein saidpolymonoolefin bonding melt is melt extruded at a melt temperature ofabout 350* to 700* F., and applied in a range of about 3 to 16 pounds ofsaid melt per 3000 square foot-ream of said substrate.
 14. The processaccording to claim 13 wherein said substrate is pretreated with apolyalkyleneimine at a rate of about 0.5 to 5 pounds per ream employingsaid polyalkyleneimine as a hydrocarbon solution thereof, so as to applyabout 0.01 to 0.1 pound per ream on a dry solids basis.
 15. The processaccording to claim 14 wherein said subStrate is a Kraft paper, said filmis a biaxially oriented polypropylene film, said melt flow bonding is apolypropylene.
 16. The process of claim 7 wherein each saidpolymonooolefin is selected from homopolymers of propylene andcopolymers of ethylene-propylene.
 17. The process of claim 1 whereinsaid sheet is conveyed by a first roller means; said film is conveyed bya second roller means; said first and second roller means define or niparea therebetween, and said area of contact is defined by said nip area.